There are several things to note when clearing a cave-in; first of all, the spell must be a target spell; second of all, the rocks may be launched at a high velocity, and can be very dangerous, so it is suggested that you step away from the opening of the blocked area. Rocks may be launched upward into a cavity in the ceiling and may fall several seconds later — this can be dangerous as well, so make sure to have waited a while before entering. This may also dislodge some movable loot and it can get lost if it is hit with the effect. This may alert enemies of your presence, and may damage familiars. When casting the spell, make sure to fire it behind the blockage, or it may jam it up even more.